The largest hypertension study ever conducted has found that the simple "water pill" is preferred to newer, more popular and expensive drugs and should be the designated choice "for use in starting treatment for high blood pressure."

But what if you're among the 24 million Americans taking other types medications to manage hypertension? Should you talk to your doctor of switching to a diuretic (water pill), whose use has dwindled in recent decades with the introduction of newer drugs?

"Yes," says the lead researcher of this landmark study, called ALLHAT for the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial.

"The bottom line of our study is that diuretics should be considered as the first step for treating all new cases of hypertension," Barry R. Davis, MD, PhD, of the University of Texas School of Public Health, tells WebMD. "But diuretics should also be part of every hypertensive regimen."

Davis adds that while the study findings recommend using diuretics to start treatment of high blood pressure, it shouldn't be interpreted to suggest that only newly diagnosed patients would benefit from them.

"The way the clinical trail was conducted, 90% of the study participants had been on some type of medication [before the study], and their medication was stopped and they were switched to four different drugs in randomized fashion -- including the diuretic," he says. "And those taking the diuretics, which are much less expensive, fared as good or better."

Plus, they don't cause any additional side effects than the other drugs -- typically increased urination that subsides after several weeks, and sometimes dizziness, muscle weakness, and cramps. "In rare cases, someone can't take them because they may be allergic to them," says Davis. "But for the average patient, they are the better choice. So if you are on another medication and your blood pressure is not controlled, and another medication has to be added, as is often the case, it should be a diuretic."

The results of the eight-year ALLHAT trial, released recently in the Journal of the American Medical Association, brings new attention to this old standard in blood pressure treatment, which works by ridding the body of excess salt and water. The generic diuretic used in the study, chlorthalidone, was deemed a better choice than two other types of treatments that can cost as much as 30 times more --- the ACE inhibitorsPrinivil or Zestril and the calcium channel blocker Norvasc. A third medication, the alpha-blocker Cardura, was dropped from the study some two years ago because it increased the risk of heart disease and stroke in study participants.